Use of self-assembled nanoporous glass colloids for prolongation of plasticity of polymeric materials

ABSTRACT

This invention describes the encapsulation of and self-assembly of meso (nano) porous silica particles from inorganic an inexpensive silica precursor, sodium silicate. The particles have a well defined shape, high surface area, and high uniformity of the pore size, the properties that are typically found for high quality mesoporous material synthesized from organic silica precursors. The disclosure illustrates a synthesis of hard spheres, discoids, and a mixture comprising discoids, gyroids and fibers, termed as origami.

CROSS REFERENCE TO CO-PENDING AND PRIOR APPLICATIONS

The present application is a continuation-in-part of Ser. No. 12/229,001('001) filed on Aug. 19, 2008 entitled Synthesis of Mesoporous SilicaShapes Using Sodium as a Silica Source. This application claims thebenefit of Provisional Application 60/996,836 filed on by Sokolov andNaik on Dec. 7, 2007.

GOVERNMENT RIGHTS

This invention was made with government support under Grant NumberW911NF-05-1-0339 awarded by US Army Research Office. The government hascertain rights in the invention.

FIELD OF INVENTION

Self-recovery of deterioration of plasticity of polymeric compositematerials based on having small colloidal particles or fibers which aretypically used for the reinforcement of polymeric composed materials,filled with a plasticizer. An economical approach is to usemicrometer-sized meso (nano) porous silica particles in various shapesfrom an inexpensive inorganic silica precursor, sodium silicate.

BACKGROUND OF THE INVENTION

Plasticized polymeric compositions have good physical-mechanicalproperties and are particularly useful for various applications, such assheathings of various cables and protective coating for moving parts.Typically plasticizers are added as solvents. The major problem with theuse of plasticizers is their limited lifetime. Polymers, beingintrinsically transparent for various oxidation and deterioration,cannot protect plasticizers from degradation. Biodegradation ofplasticizers is also a known serious problem as disclosed by Pi-Dong Gu,in International Biodeterioration Biodegradation Volume 59, Issue 3,April 2007, Pages 1701791.

An economical approach is to use micrometer-sized meso (nano) poroussilica particles in various shapes from an inexpensive inorganic silicaprecursor, sodium silicate. The use sodium silicate is discussed below.

-   -   Mesoporous silica as discussed by: T. Yanagisawa et al.        (1), C. T. Kresge et al. (2), and J. S. Beck et al. (3), (listed        in the reference list below and incorporated herein by        reference) is an important class of self-assembled inorganic        materials consisting of regularly arranged mesoporous channels        in the amorphous silicon dioxide network. Because of their large        specific surface area, high pore volume, uniform pore diameter        and high thermal stability, mesoporous silica has been envisaged        to be a promising material in adsorption, catalysis, and ultra        filtration, so also as a host for deposition of clusters,        nanodots and nanowires, etc.

Mesoporous silica exhibiting lamellar, hexagonal (p6mm), or cubic (Ia3d,Im3m, Pm3n, etc.) structures and presenting a host of pore arrangementshave already been prepared under different preparative conditions. SeeT. Yanagisawa et al. (1), C. T. Kresge et al. (2), J. S. Beck et al.(3), D. Zhao et al (4), D. Zhao et al. (5), and H. Yang et al. (6), (alllisted below and all incorporated herein by reference). It has beenrealized that the control over the particle morphology and the internalmesoporous architecture could open up new possibilities for their usageas a carrier for functional molecules for advanced applications inlasers and optics. For example, see B. J. Scott et al. (7), F. Marlow etal. (8), and I. Sokolov et al. (9), all listed in the reference listbelow and all hereby incorporated herein by reference. Previously,mesoporous silica particles of different morphology have beensynthesized using alkyl orthosilicates as silica source together withionic or block copolymer surfactants as structure directing agents(SDAs) under basic or acidic preparative conditions. See G. A. Ozin etal. (10), Q. Huo et al. (11), S. Schacht et al. (12), X. Pang et al.(13), K. Kosuge et al. (14), X. Pang et al (15), S. Han et al. (16), S.P. Naik et al. (17), and Y. S. Lin et al (18), all listed in thereference list below and all hereby incorporated herein by reference.However, due to their high costs, storage and handling problems,replacement of alkysilicates by other economical and more robust sourcesof silica is much desired to realize their anticipated commercialapplications. See A. Berggren et al listed in the reference list belowand hereby incorporated herein by reference. Sodium silicates representan example of economical and robust sources of silica. There havealready been several reports on the synthesis of mesoporous silicafibers and spheres using sodium silicates as a silica source. See X.Pang et al., K. Kosuge et al., X. Pang, et al., S. Han et al., and S. P.Naik et al. listed in the reference list below and all herebyincorporated herein by reference. Nonetheless, many of these methodsinvolve use of organic solvents or mixtures of surfactants and complexprocedures for the synthesis of mesoporous silica particles. Moreover,synthesis of well-formed mesoporous silica particles having a circularinternal architecture and pore channels running around the particle axisusing sodium silicate as a silica source has not been reported usinginorganic silica sources. Mesoporous silica with such morphology isuseful in applications involving maximum retention of the occludedspecies inside the mesostructure for an extended period of time. See I.Sokolov et al. listed in the reference list below and herebyincorporated herein by reference.

SUMMARY

This disclosure describes a self-recovery of deterioration of plasticityof polymeric composite materials based on having small colloidalparticles or fibers which are typically used for the reinforcement ofpolymeric composed materials, filled with a plasticizer. An economicalapproach is to use micrometer-sized meso (nano) porous silica particlesin various shapes from an inexpensive inorganic silica precursor, sodiumsilicate.

Additionally this disclosure describes a novel method for the synthesisof micrometer-sized meso (nano) porous silica particles in variousshapes from an inexpensive inorganic silica precursor. The disclosureillustrates a synthesis of hard spheres, discoids, and a mixturecomprising discoids, gyroids and fibers, termed as origami. Theparticles have a well defined shape, high surface area, and highuniformity of the pore size, the properties that are typically found forhigh quality mesoporous material synthesized from organic silicaprecursors.

The process includes preparation of nanoporous silica particles, eitherfibers or discoids or a mix of fibers and discoids using an inorganicsilica precursor such as a sodium silicate. The structure directed agent(SDA) is chosen among either ionic or copolymer surfactants or a mix ofthe above. Specific examples of surfactant can be eithercetyltrimethylammonium chloride or cetyltrimethylammonium bromide orplurionic acid.

The condensation catalyst is chosen among strong acids comprising ofhydrochloric or nitric or sulfuric or phosphoric acids, or a mix of theabove.

The synthesis is carried out using the molar sol composition:1Na2SiO3.9H20:X CTAC:Y HCl:Z H2O. X can be chosen as any from the range0.5-3, and Y can be chosen as any from the range 10-70, and Z can bechosen as any from the range 600-800. The surface areas of the obtainedparticles are higher than 1000 m²/g; pore diameters are 2.4-2.5 nm, andpore volumes are 0.93 cm³-0.96 cm³/g. The process is done in roomtemperature (15-25° C.) to synthesize preferentially fibers. The processis done at 60-90° C. temperature to synthesize preferentially discoids.The preparation of nanoporous silica particles, either spheres, ordiscoids, or origami-type, use an inorganic silica precursor, such assodium silicate. The structure directed agent (SDA) is chosen amongeither ionic or copolymer surfactants or a mix of the above. Thesurfactant can be either cetyltrimethylammonium chloride orcetyltrimethylammonium bromide or plurionic acid.

The condensation catalyst is chosen among strong acids comprising ofhydrochloric or nitric or sulfuric or phosphoric acids, or a mix of theabove. The synthesis of spheres is carried out using the following themolar sol composition: 1Na2SiO3.9H20:X HCHO:Y CTAC:210 H2O. X can bechosen as any from the range 5-32 and Y can be chosen as any from therange 0.5-0.8. The synthesis of spheres is carried out using molar solcomposition: 1Na2SiO3.9H20:22 HCHO:0.5 CTAC:210 H2O. The surface area ofthe spheres is at least 600 m²/g, the pore diameter and pore volumes are3.3 nm, and 0.3 cm³/g, respectively.

The synthesis of discoids synthesized from the sols of molarcompositions 1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl. The synthesis oforigami particles is synthesized from the sols of molar compositions1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O:16 HCl. The surface areasof the particles is at 500-900 m²/g, where as the pore diameter andvolume are in the range of 2.4-3.3 nm, and 0.2-0.4 cm³/g, respectively.

With this process the surface areas of the particles is at 500-900 m²/g,where as the pore diameter and volume are in the range of 2.4-3.3 nm,and 0.2-0.4 cm³/g, respectively.

A second process of synthesizing mesoporous silica fibers and discoidsalso uses disodium trioxosilicate (Na2SiO3.9H20) as an silica source;cetyltrimethylammonium chloride (or bromide) (CTAC, 25% aqueous) as astructure directed agent (SDA) in a presence of hydrochloric acid as acatalyst, wherein a molar sol composition is at the range of1Na2SiO3.9H20:0.5-3 CTAC:10-70 HCl:600-800H20. The process includesfixing the molar sol composition at 1Na2SiO3.9H20:1.5 CTAC:28 HCl:730H20.

The process further includes dissolving 1.6 g of Na2SiO3.9H20 in 55.2 gH2O in a high density polypropylene (HD-PP) bottle and stirring for 15minutes. Then slowly adding 16 g of concentrated HCl 11.2 g CTAC in aHD-PP bottle and stirring for 2 minutes. This is followed by slowlyadding said clear sodium silicate solution to said CTAC/HCl solution andstirring for 5 minutes and maintaining a resulting sol at fixedtemperature between 4°-70° C., depending on the desired ratio betweenfibers and discoids for 6-24 hours under quiescent conditions (standingsteady, with no external mixing of shaking). This is followed byrecovering a product by filtration, then washing several times withdistilled water, and subsequently, drying for several hours.

A next process of synthesizing mesoporous silica particles also usingdisodium trioxosilicate (Na2SiO3.9H20) as a silica source,cetyltrimethylammonium chloride (CTAC, 25% aqueous) as a structuredirected agent (SDA) in the presence or absence of formamide andhydrochloric acid as a catalyst. The process of synthesizes mesoporoussilica spheres in the absence of HCl from sols of molar compositions1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O. A preferred sol of molarcomposition is 1Na2SiO3.9H20:22 HCHO:0.5 CTAC:210 H2O. For the synthesisof discoids, the process uses a molar composition of the sol maintainedat 1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl. For the synthesis oforigami shapes, the process uses a molar composition of the solmaintained at 1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O:16 HCl.

DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1(A) illustrates an scanning electron microscopy (SEM) image of amixture of mesoporous silica fibers synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H2O at 25° C., 24 hours;

FIGS. 1 (B) and (C) illustrate mesoporous silica discoids synthesizedfrom the same sol but at a range between 70° C. and 90° C., 24 h;

FIG. 1(D) illustrates calcined discoids;

FIG. 2 illustrates the x-ray diffraction (XRD) pattern of the mesoporoussilica fibers (A) and discoids (B) synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H2O, at 25° C., 24 h and70° C., 24 hours, respectively.

FIG. 3(A) and FIG. 3(B) illustrate transmission electron microscopic(TEM) images of the fibers (A) and discoids (B), showing the internalcircular architecture and pore channels running around the particleaxis.

FIG. 4 illustrates N2 adsorption/desorption isotherm measured at 77 K oncalcined mesoporous silica fibers synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H2O at 25° C., 24 hours,with inset (B) illustrating the pore size distribution for the discoids;

FIG. 5 illustrates N2 adsorption/desorption isotherm measured at 77 K oncalcined mesoporous silica discoids synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H20 at 70° C., 24 hours,with insets (B) illustrating the pore size distribution for thediscoids;

FIG. 6 illustrates confocal laser microscopy images at differentmagnifications of the dye filled mesoporous silica discoids synthesizedfrom the sol of molar composition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729H20:0.002 R6G at 70° C., 24 h with inset (B) illustrating a magnifiedimage showing the coiled silica tubes forming discoids;

FIGS. 7 (A)-(B) illustrate optical images of the as-synthesized andcalcined spheres obtained from the sol of molar composition1Na2SiO3.9H20:21.69 HCHO:0.51 CTAC:210 H2O with the inset (C) inillustrating the scanning electron microscopy (SEM) image of anindividual broken sphere;

FIGS. 7 (D) and (E) illustrate the transmission electron microscopic(TEM) images of the spheres;

FIGS. 8 (A)-(C) illustrate the x-ray diffraction (XRD) patterns of thespheres, discoids and origami particles synthesized from the sols ofmolar compositions 1Na2SiO3.9H20:5.21-31.51 HCHO:0.56-0.77 CTAC:210 H2O;1Na2SiO3.9H20:0.56-0.77 CTAC:210 H2O:16.35 HCl, and1Na2SiO3.9H20:5.21-31.51 HCHO:0.56-0.77 CTAC:210 H2O:16.35 HCl,respectively.

FIGS. 9 (A) and (B) illustrate the confocal microscopy images ofdiscoids and origami particles synthesized from the sols of molar1Na2SiO3.9H20:0.56-0.77 CTAC:210 H2O:16.35 HCl and1Na2SiO3.9H20:5.21-31.51 HCHO:0.56-0.77 CTAC:210 H2O:16.35 HCl,respectively, with insets in the images displaying individual particles;

FIG. 10 illustrates a cross-sectional transmission electron microscopic(TEM) image of the gyroids particle synthesized from the sol of molarcomposition 1Na2SiO3.9H20:0.56-0.77 CTAC:210 H2O:16.35 HCl;

FIG. 11 illustrates a N2 adsorption/desorption plot;

FIG. 12 illustrates an SEM image of parallel nanochannels in fiber likeANSC of uniform shape; and

FIG. 13 illustrates SEM images of self-assembled nano-glassfiber-capsules.

DESCRIPTION

In this invention we use existing plasticizers encapsulated insidenanoporous glass colloids. Such encapsulation protects the plasticizersfrom deterioration, limits their bio-availability. Such particles aredescribed in a number of publications and patent applications includingS. P. Naik, Igor Sokolov, “Room Temperature Synthesis of NanoporousSilica Spheres and their Formation Mechanism” Solid StateCommunications, 2007 Volume 144. Issues 10-11, December 2007, Pages417-440: S. P. Naik, S. P, Elangovan T. Okubo, and Igor Sokolov“Morphology Control of Mesoporotes Silica Particles”. Journal ofPhysical Chemistry (C), v. 111, n. 30, pp. 11168-11173, 2007: Sokolov,I. and Y. Kievsky, 3D Design of Self Assembled. Vanoporous Colloids.Studies in Surface Science and Catalysis, 2005 v. 156, pp. 433-443,2005); Ya. Kievsky and I. Sokolov Self-Assembly of uniform NanoporousSilica Fibers, IEEE Transactions on Nanotechnology, v. 4 (5), pp.490-494; Sokolov, Ya. Kievsky, “Self-Assembly of Nanoporous SilicaFibers of Uniform Shape”, approved as pending in December 2004 U.S.60/631,224. All of the above references are hereby incorporated hereinby reference.

In principle encapsulation of plasticizers could be done with anycapsules. However, it would be economically advantageous to so with onesmade with sodium silicate. Below is described is the synthesis oftnesoporous silica shapes using sodium silicate as a silica source.

The particles fibers and mechanically robust and have enough empty areainside of the cylindrical porous to keep plasticizers inside. Examplesof such particles are shown in FIGS. 12 and 13

The top portion of FIG. 12 illustrates the SEM image of parallelnanochannels in fiber like ASNC of uniform shape. A large area (leftbar-size is 22 gm) and zoom to a few ASNC (right, bar-size is 5 gm). Themiddle portion illustrates a TEM image of near the ASNC edge showingperiodicity about 3.6 nm (left), a schematics showing the arrangement ofnanochannels in silica matrix (right). Bottom Portion: XRD of the ASNCsflat) and distribution of the inner tube diameters (right) [V. V.Kievsky, B. Carey, S. Naik, N. Mangan, D. ben-Avraharn, and I. Sokolov,J. Chem. Phys. 128, 151102 (2008) hereby incorporated herein byreference].

FIG. 12, illustrates SEM images of self assembled nanoporous glass fibercapsules. FIGS. 12 (a) and (b) illustrate examples of differentsyntheses (bar size is 11 pm.

The use of the above silica colloids/fibers strengthens the material.Therefore the amount of encapsulated plasticizer can be increased andconsequently, results in the further extension of the plasticizingaction. In addition due to decreased bio degradation of the degradationof the plasticizers antibacterial substances can be added inside thesame capsules.

Herein we disclose of the synthesis of a procedure nanoporous silicaparticles of various shapes using sodium silicate (disodiumtrioxosilicate is a particular example) as a silica source as aneconomical choice to use micrometer-sized meso (nano) porous silicaparticles in various shapes from an inexpensive inorganic silicaprecursor, sodium silicate. It is a robust process. We demonstrate thatby adjusting the reaction sol composition, hard spheres, discoids or amixture of various shapes, termed as origami, comprising gyroids, fibersand discoids can be obtained. The description below uses numbers asexemplary values.

Example 1: Synthesis of Fibers and Discoids

Mesoporous silica fibers and discoids are synthesized using disodiumtrioxosilicate (Na2SiO3.9H20) as the silica source;cetyltrimethylammonium chloride (or bromide) (CTAC, 25% aqueous) as anexample of the structure directed agent (SDA) in the presence ofhydrochloric acid as an example of a catalyst. The molar sol compositionis at the range of 1Na2SiO3.9H20:0.5-3 CTAC:10-70 HCl:600 800H20. Forthe example given below, it is fixed at, 1Na2SiO3.9H20:1.5 CTAC:28HCl:730H20. Typically, 1.6 g of Na2SiO3.9H20 is dissolved in 55.2 g H2O,taken in a high density polypropylene (HD-PP) bottle, understirring for15 minutes. Separately, 16 g of concentrated HCl is slowly added to 11.2g CTAC taken in HD-PP bottle and stirred for 2 minutes. The clear sodiumsilicate solution is then slowly added to CTAC/HCl solution and stirredfor 5 minutes. The resulting sol is maintained at fixed temperature ±15°C.+70° C., depending on the desired ratio between the fibers anddiscoids) for 3-24 hours under quiescent conditions. The product isrecovered either by filtration (for example, using a Buckner funnelunder vacuum) or by centrifugation, then washed several times withdistilled water, and subsequently, dried at for several hours. Dependingon the desired applications, the as-synthesized discoids can be useddirectly, or calcined through a procedure known to one skilled in art.To characterize the particles, the powder x-ray diffraction (XRD)patterns on the particles are collected on a Bruker D8 X-Raydiffractometer using Cuka radiation (40 kV, 40 mA). The scanningelectron microscopy (SEM) images are collected on a JEOL 6300 instrumentoperating at 15 kV. Prior to the measurements, the samples are coatedwith gold for 1 minute in an Amatech hummer 6.2 sputtering systemoperating at 40 millitorr. The transmission electron microscopic (TEM)images of the calcined particles are recorded on a JEM 2010 electronmicroscope (JEOL) at an acceleration voltage of 200 kV. The samples areprepared by dispersing the calcined material in water at roomtemperature. A few drops of this dispersion were placed on a holeycarbon-coated mesh and dried at room temperature. The N2adsorption/desorption isotherms of the calcined mesoporous silicasamples are measured at 77 K on a NOVA 1200e instrument (QuantachromeCo.). Before the measurement, samples are degassed at 350° C. and 10 Pafor at least 12 h. The confocal laser microscopy images of thefluorescent particles are taken on a Nikon, D-Eclipse C1-Microscope.Rhodamine 6G (R6G, Exciton) fluorescent dye filled mesoporous silicadiscoids are prepared from the sol of molar composition1Na2SiO3.9H20:1.5 CTAC:28 HCl:729H20:0.002 R6G, that is the same asabove, except for the addition of the dye. The dye is at first dissolvedin water together with sodium silicate and the resulting solution isadded to CTAC/HCl sol, as described above.

The morphology of the synthesized mesoporous silica particles isstrongly dependent upon the molar composition of the synthesis sol usedin this example. The mostly well-formed fibers of varying sizes as shownin the scanning electron microscopy (SEM) image of FIG. 1 (A) areobtained at room temperature from the sol of molar composition1Na2SiO3.9H20:1.5 CTAC:28 HCl:7301120. We have observed that this lowcurvature fibers begins to disappear with concomitant formation of highcurvature and well-formed, single-crystal like 3-5 pm sized discoidsupon increasing the synthesis temperature [See FIGS. 1 (B)-(C)] andeventually the fiber to discoid transformation is complete at synthesistemperatures between 60 to 90° C.

FIG. 1 illustrates scanning electron microscopy (SEM) images of (A)mixture of mesoporous silica fibers synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H₂O at 25° C., 24 hoursand FIGS. 1 (B) and (C) illustrate mesoporous silica discoidssynthesized from the same sol but at a range between 70 C and 90° C., 24h (D) calcined discoids.

The hexagonal p6mm structure of the fibers and discoids is establishedfrom x-ray diffraction (XRD) measurement as illustrated by the patternsin FIGS. 2 (A) and (B), respectively. The d100 spacing of ca. 46 A and47 A was obtained for fibers and discoids, respectively. Calcination atup to 500° C. does not have any noticeable effect on the morphology ofthe particles as confirmed by the scanning electron microscopy (SEM)images of as-formed and calcined discoids illustrated in FIGS. 1 (C) and(D), respectively.

FIG. 2 illustrates an x-ray diffraction (XRD) pattern of the mesoporoussilica fibers (A) and discoids (B) synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H2O, at 25° C., 24 hoursand 70° C., 24 hours, respectively.

The pore architecture in the particle mesostructure is established fromthe transmission electron microscopic (TEM) images for fibers anddiscoids shown in FIG. 3. These images present a well-organized,hexagonal, p6mm structure with hexagonally organized pores and possess acircular architecture with pore channels running around the fiber ordiscoid axis endowing self-sealed structure to the particles. Thediameter of the channels obtained from transmission electron microscopic(TEM) was found to be well in agreement with that obtained from N2adsorption/desorption measurement vide infra.

FIG. 3 illustrates transmission electron microscopic (TEM) images of thefibers (A) and discoids (B), showing the internal circular architectureand pore channels running around the particle axis. The mesoporoussilica fibers and discoids were synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729H20 at 25° C., 24 hours and70° C., 24 hours, respectively. The insets here are the schematics offibers and discoids, respectively.

A nitrogen adsorption/desorption measurement conducted at 77.3 K on thecalcined fibers and discoids gives type IV isotherms as shown in FIGS. 4and 5, respectively.

There is little difference between the texture properties of fibers anddiscoids. Both the isotherms showed a step rise at −0.2 P/Po with littlehysteresis, that is typical of high quality mesoporous materials. Themesopore size is estimated, see FIGS. 4 (B) and 5 (B), from theadsorption branch of the isotherm according to the correlation obtainedfrom Nonlinear Fluctuation-Dissipation Theorem (NLDFT) theory. See A. V.Neimark et al., and M. Jaroniec et al., both listed in the referencelist below and both hereby incorporated herein by reference. For fibersand discoids, the BET surface areas are 1330 and 1250 m²/g; mesoporediameters are 2.4 nm and 2.5 nm, and pore volumes are 0.93 cm³ and 0.96cm³/g, respectively.

FIG. 4 illustrates N2 adsorption/desorption isotherm measured at 77 K oncalcined mesoporous silica fibers synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:28 HCl:729 H₂O at 25° C., 24 h. Inset(B) illustrates the pore size distribution for the discoids.

FIG. 5 illustrates N2 adsorption/desorption isotherm measured at 77 K oncalcined mesoporous silica discoids synthesized from the sol of molarcomposition 1Na2SiO3.9H20:1.5 CTAC:281-1Cl:729H20 at 70° C., 24 h. Inset(B) illustrates the pore size distribution for the discoids.

To elucidate further, the coiling of fibers, the R6G dye loaded discoidsare observed by confocal laser microscopy. These images, illustrated inFIG. 6, confirm the coiled macroscopic domains in the discoids as shownby the bright fluorescence of the curled up coiled rods, indicated byarrows in FIG. 6 (B). This result is also in agreement with the scanningelectron microscopy (SEM) and transmission electron microscopic (TEM)observations. Moreover, higher temperature promotes formation of curvedfibers by balancing free energy of the fibers with the entropic term asreported earlier See Y. Kievsky et al. and I. Sokolov et al. both listedin the reference list below and both hereby incorporated herein byreference.

FIG. 6(A) illustrates confocal laser microscopy images at differentmagnifications of the dye filled mesoporous silica discoids synthesizedfrom the sol of molar composition 1Na2SiO3.9H20:1.5 CTAC:28HCl:729H20:0.002 R6G at 70° C., 24 hours. Inset (B) is a magnified imageillustrating the coiled silica tubes forming discoids.

Thus, the method described above synthesizes mesoporous single-crystallike with hexagonally organized pores and possess a circulararchitecture with pore channels running around the fiber or discoidendowing self-sealed-type structure to the particles. For fibers anddiscoids of this Example 1, the BET surface areas are 1330 m²/g and 1250m²/g; mesopore diameters are 2.4 nm and 2.5 nm, and pore volumes are0.93 cm³ and 0.96 cm³/g, respectively.

Example 2: Synthesis of Spheres, Discoids, Fibers

In this Example 2, mesoporous silica particles are synthesized by usingdisodium trioxosilicate (Na2SiO3.9H20, Fishcer Scientific) as the silicasource, cetyltrimethylammonium chloride (CTAC, 25% aqueous, Aldrich) asan example of the structure directed agent (SDA) in the presence orabsence of formamide (Aldrich) and hydrochloric acid (J T Baker) as acatalyst.

Mesoporous silica spheres can be synthesized in the absence of HCl fromsols of molar compositions 1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O;spheres exemplified here are prepared from the sol of molar composition1Na2SiO3.9H20:22 HCHO:0.5 CTAC:210 H2O.

For the synthesis of discoids, the molar composition of the sol ismaintained at 1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl; whereas,origami shapes are synthesized from the sol of molar composition1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O:16 HCl.

A calculated amount of Na2SiO3.9H20 is dissolved in distilled waterunder stirring for 15 minutes, CTAC solution is then slowly added,followed by the addition of HCHO and/or HCl, whenever required. Thestirring is continued for another several minutes. The clear sol thusformed is maintained at room temperature, without stirring, for durationof between several hours to one week. The product is recovered either byfiltration (for example, using a Buckner funnel under vacuum) or bycentrifugation, then washed several times with distilled water, andsubsequently, dried for several hours. Depending on desiredapplications, the as-synthesized discoids can be used directly, orcalcined through a procedure known to one skilled in art.

To characterize the collected product, the powder x-ray diffraction(XRD) patterns on the as-synthesized materials are collected on anMO3X-HF (Bruker AXS) instrument using CuKa radiation (40 kV, 40 mA). Thescanning electron microscopy (SEM) images are collected on a JEOL 6300instrument operating at 15 Kv. Prior to the measurements, the samplesare coated with gold for 1 minute in an Anatech hummer 6.2 sputteringsystem operating at 40 millitorr. The transmission electron microscopic(TEM) images of the calcined particles are recorded on a JEM 2010electron microscope (JEOL) at an acceleration voltage of 200 kV.

The samples for characterization are prepared by dispersing the calcinedmaterial in water at room temperature. A few drops of this dispersionwere placed on a holey carbon-coated mesh and dried at room temperature.Dynamic light scattering (DLS) measurements on the sol are performedusing BIC model 90Plus Particle Size Analyzer at 20° C. Opticalmicroscopy, scanning electron microscopy (SEM) and transmission electronmicroscopic (TEM) images of the as-synthesized and calcined spheressynthesized from the sol of molar composition 1Na2SiO3.9H20:21.69HCHO:0.51-CTAC:210 H2O, are illustrated in FIGS. 7 (A)-(B), 7 (C), and(D,E), respectively.

There is no obvious change in the morphology of the spheres aftercalcination. However, a few spheres have been found to be damaged orbroken, as illustrated in the inset scanning electron microscopy (SEM)image of FIG. 7 (C). The average size of the spheres was ca. 4-6 p.m.The spheres are hard and have a dense internal structure as confirmedfrom the transmission electron microscopic (TEM) image in FIG. 7 (D).The mesoporous structure in the surface of the sphere is confirmed fromthe transmission electron microscopic (TEM) image illustrated in FIG. 7(E). Although spheres can be synthesized under a range of molarcompositions 1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O, their sizeand distribution is strongly dependent on the sol's molar composition.For example, doubling the amount of formamide will decrease the averagediameter of the spheres by −2 pm.

The mesoporous structure of the spheres is confirmed from the x-raydiffraction (XRD) pattern illustrated in FIG. 8 (A). The dio-spacing ofca. 44 A is obtained, corresponding to the hexagonal p6mm structure.

FIG. 7 (A)-(B) illustrate the scanning electron microscopy (SEM) imagesof the as-synthesized and calcined spheres obtained from the sol ofmolar composition 1Na2SiO3.9H20:21.69 HCHO:0.51 CTAC:210 H2O. Figure (C)and (D) are the transmission electron microscopic (TEM) images of thespheres. The inset in FIG. 7(B) is the scanning electron microscopy(SEM) image of an individual broken sphere.

FIGS. 8 (A)-(C) illustrate the x-ray diffraction (XRD) patterns of thespheres, discoids and origami particles synthesized from the sols ofmolar compositions 1Na2SiO3.9H20:5-32 HCHO:0.5-0.8 CTAC:210 H2O;1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl, and 1Na2SiO3.9H20: 5-32HCHO:0.5-0.8 CTAC:210 H2O:16 HCl, respectively.

The discoids and origami particles obtained here have been employed forencapsulating florescent dyes in the mesochannels channels. The confocalmicroscopy images of these particles are illustrated in FIGS. 9 (A) and(B), respectively. The strong fluorescence radiated by these particlesis very clear from these images. The morphologies of the discoid andsome of the origami particles are also shown as insets of the FIGS. 9(A)and (B), respectively.

The hexagonal p6mm structure of the discoids and origami particles isconfirmed from their x-ray diffraction (XRD) patterns shown in FIGS. 8(B) and (C), respectively.

The dio-spacings of ca. 47 A and 45 A is obtained for gyroids andorigami, respectively.

As confirmed from the cross-sectional transmission electron microscopic(TEM) image illustrated in FIG. 10 of the discoids, the mesoporouschannels indeed run in circular or concentric fashion.

FIGS. 9 (A) and (B) illustrate the confocal microscopy images ofdiscoids and origami particles synthesized from the sols of molar1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl and 1Na2SiO3.9H20:5-32HCHO:0.5-0.8 CTAC:210 H2O:16 HCl, respectively. The insets in the imagesof FIG. 9(B) display individual particles.

FIG. 10 illustrates the cross-sectional transmission electronmicroscopic (TEM) image of the gyroids particle synthesized from the solof molar composition 1Na2SiO3.9H20:0.5-0.8 CTAC:210 H2O:16 HCl.

BET (gas absorption) measurements, illustrated in FIG. 11, demonstratethat bulk mesoporous material has been produced. FIG. 11 is a N2adsorption/desorption plot (the type of the plot is indicative ofmesoporous material).

From the above measurements, one can find that for the spheres, thesurface area of the spheres is at least 600 m²/g, the pore diameter andpore volumes are 3.3 nm, and 0.3 cm³/g, respectively. For discoids andorigami, the surface areas of the particles is at 500900 m²/g, where asthe pore diameter and volume were in the range of 2.4-3.3 nm, and0.2-0.4 cm³/g, respectively.

The particles synthesized by the processes described can be used: as afiller for chromatography columns; for slow release of various chemicals(slow drug release) or as absorbents for various chemicals such asantibacterial agents, anti-rusting, or glue for self-healing materials,etc.

The illustrative embodiments and modifications thereto describedhereinabove are merely exemplary. It is understood that othermodifications to the illustrative embodiments will readily occur topersons of ordinary skill in the art. All such modifications andvariations are deemed to be within the scope and spirit of the presentinvention as will be defined by the accompanying claims.

REFERENCES

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We claim:
 1. A method of preparing nanoporous silica particles whichprolong the plasticity of a polymer material after being added to thesaid polymer material, the nanoporous silica particles comprisingnanoporous silica fibers, nanoporous silica discoids, or a mix ofnanoporous silica fibers and nanoporous silica discoids, the methodcomprising the steps of: combining an inorganic silica precursor, sodiumsilicate, with an aqueous solvent, an acidic catalyst, and a structuredirected agent (SDA) to form a precursor solution; creating, using saidprecursor solution and a molecular self-assembly process, particleschosen from nanoporous silica fibers, nanoporous silica discoids, and/ora mixture of nanoporous silica fibers and discoids, said nanoporoussilica fibers and/or discoids having a porosity in the range of 2-10nanometers, and having a surface area greater than 500 m²/gram, whereinsaid molecular self-assembly process is carried out using a molar solcomposition: 1 mol Na₂SiO₃.9H2O:X mol cetyltrimethylammonium bromide(“CTAB”):Y mol HCl:Z mol H₂O; calcining the obtained particles; andadding and retaining a plasticizer inside one or more pores of saidnanoporous silica fibers and/or discoids, wherein capture within saidone or more pores prolongs plasticity of said polymer material, andwherein X is chosen as any from a range of approximately 0.5-3 mol, andY is chosen as any from a range of approximately 10-70 mol, and Z ischosen as any from a range of approximately 600-800 mol.
 2. The methodof claim 1 wherein said structure directed agent (SDA) is an ionicsurfactant, a copolymer surfactant, or a mixture of ionic and copolymersurfactants.
 3. The method of claim 1, wherein said precursor solutionfurther comprises condensation catalyst, the condensation catalystselected from the group consisting of hydrochloric acid, nitric acid,sulfuric acid, phosphoric acid, and a combination thereof.
 4. The methodof claim 1, wherein said molecular self-assembly process is performed atroom temperature (15-25 degrees C.) to synthesize fibers.
 5. The methodof claim 1, wherein said molecular self-assembly process is performed at60-90 degrees C. temperature to synthesize discoids.